One of the interesting bits of Dan Ariely's Predictably Irrational is the emphasis on how rationality changes along with emotional state. To test this, Ariely and some colleagues devised an experiment in which they asked a set of men attending UC Berkeley to answer a variety of questions on sexual preference. Then they paid them to repeat the experiment, only this time, the questions would pop up on the computer while they were masturbating to pornography (quite a test, right). The results are pretty startling. Not only did the answers to the same questions, by the same people, change, but they changed drastically. Sometimes, the percent answering "yes" to a certain practice jumped by as much as 420 percent (sadly, that question was "would you slip a woman a drug t increase the chance that shed have sex with you?"). More often, kinks became more arousing (22 percent of masturbating males found cigarette smoke to be an aphrodisiac, while only 13 percent answer affirmatively in the cold state) and behavior grew riskier (lower adherence to condoms, etc). I've graphed some of the results below, but the chart was too big to put in the post. So click on it for a full-size version:
The implications of this are significant. Someone desperate for money to pay the rent or purchase a home is less rational when they meet a loans counselor, someone terrified of a cancer diagnosis is less likely to prove an effective comparison shopper. I'd argue that we're rarely rational creatures, but insofar as we do have a rational side, its pretty context contingent, and can easily be overwhelmed by our passions, fears, and, yes, arusal.
The implications of this are significant. Someone desperate for money to pay the rent or purchase a home is less rational when they meet a loans counselor, someone terrified of a cancer diagnosis is less likely to prove an effective comparison shopper. I'd argue that we're rarely rational creatures, but insofar as we do have a rational side, its pretty context contingent, and can easily be overwhelmed by our passions, fears, and, yes, arusal. 
